It used to be that every pregnant woman over age 35 was offered an amniocentesis because of her age-related increased risk for having a baby with a genetic defect. Weighing the benefits of learning genetic information versus the potential risk to the pregnancy is a difficult decision for many women. However, newer ways to screen for defects are proving attractive options.

One such alternative uses ultrasound to measure nuchal translucency, or the amount of fluid accumulating behind the fetal neck. Your doctor can combine this information with blood tests to calculate your risk as early as 11 to 13 weeks. Studies show this screening is about as accurate as the other maternal blood screening tests-spotting about 75 percent of Down syndrome pregnancies.

When a woman is pregnant, she spends a lot of time thinking about her baby. Is the baby a boy or girl? Will he or she have Daddy’s eyes or Mommy’s hair? Most of all, a woman wonders—and worries—about her unborn baby’s health. Seeking prenatal care as soon as you learn you’re pregnant is a first step toward having a healthy pregnancy and child. Over the next nine months, your doctor will order tests to detect health conditions that could affect you or your baby. Early diagnosis and treatment can help protect you both.

Some prenatal tests are given to all pregnant women. You may have additional tests depending on your medical history, family background or exam results. Some tests are diagnostic, which can reveal a specific problem; others are screenings, which can indicate whether you or your baby is at risk for a problem. Your doctor will likely recommend the following common prenatal tests.

Urine, blood and Pap tests

At your first visit, during the first six to eight weeks of your pregnancy, your doctor will test your urine to determine sugar and protein levels.

A high sugar level may indicate diabetes, and high protein may signal a urinary tract infection, kidney disease or high blood pressure. A blood test will confirm your blood type and Rh factor and check for anemia; syphilis; hepatitis B; human immunodeficiency virus; immunity against rubella, measles, chicken pox and mumps; and the presence of cystic fibrosis or sickle cell disease genes. A Pap test will screen for precancerous changes, gonorrhea and chlamydia.

Maternal serum screening

This screening test, performed at 16 to 18 weeks, checks a sample of your blood to measure one or more substances that indicate risk for some metabolic disorders, chromosomal abnormalities like Down syndrome and neural tube defects such as spina bifida. Your screening will be performed using one of the following three tests:

An AFP test will measure levels of alpha-fetoprotein, a protein made by the fetus that appears in your blood.

A quadruple screen will measure AFP, estriol, hCG and the substance inhibin-A. A positive result for any of these screenings indicates only an increased risk for these defects, not their presence in your baby.

Glucose screening

Although your doctor will test your urine for high sugar levels at every checkup, most women have a blood glucose screening at 24 weeks to check for gestational diabetes. Your doctor may order this test earlier if you’ve shown high sugar in two routine urine tests. With this test, you’ll drink a glucose solution and then have blood drawn. If your blood sugar is high, you’ll have a glucose tolerance test. You’ll drink glucose and have blood drawn once an hour for three hours.

Ultrasound

Of all the prenatal tests, the ultrasound is the one many women look forward to because it provides a first look at their baby. For this test, usually done between 16 and 18 weeks, a technician will coat your abdomen with a special gel and pass a transducer back and forth over your belly. If you need an ultrasound early in pregnancy, a special transducer inserted in the vagina may be used.

You may barely make out specific body parts from the grainy image on the screen, but a radiologist will analyze the images to determine the baby’s age, growth rate, position, movement, breathing and heart rate as well as the amount of amniotic fluid and the number of fetuses. The test may detect abnormalities such as heart defects, Down syndrome, spina bifida and gastrointestinal and kidney malformations. Often, the sex of the baby can be determined.

Group B strep

During the last few weeks of your pregnancy, your doctor will take samples from your vagina and around the perineal region to test for Group B streptococcus (GBS). This common bacterial infection is generally not serious in adults but can cause life-threatening illnesses like pneumonia or meningitis in a newborn. Between 10 percent and 30 percent of pregnant women carry the bacteria. If you test positive for GBS, treatment with antibiotics during labor and delivery will protect your baby.

Other tests you may have

Women at high risk for having a baby with chromosomal defects may be offered diagnostic tests to confirm or rule out a problem. Because these tests carry a small risk for complications like miscarriage and infection, not all women choose to have these tests:

Chorionic villus sampling (CVS). This test, performed between nine and 14 weeks, involves threading a thin tube through the cervix or a needle through the abdomen to collect a sample of tissue from the placenta. This tissue will be tested for genetic abnormalities.

Amniocentesis. During this procedure, usually performed between 15 and 17 weeks, a long needle will be inserted into your abdomen to draw a small amount of amniotic fluid from around your baby. The fluid contains cells from the baby, which will be analyzed to provide genetic information and detect chromosomal abnormalities, blood disorders and infections.